A well comprising a bore hole extending from surface to the underground formation, a casing arranged in the borehole, a tubing hanger supported at or near the top of the casing, a packer arranged in the casing at a predetermined depth, and a tubing extending from the tubing hanger to the packer. The well can be used for producing fluids from the formation. However, the well can also be use to inject fluids through the tubing into the formation, for example to enhance production.
The casing can be a single string or a set of strings one arranged inside the other, and the casing is normally fixed in the borehole by means of a layer of cement in the annulus between casing and wall of the borehole.
The invention relates in particular to the tubing through which the fluids will flow during normal operation. Normally the tubing is a steel pipe that extends from the tubing hanger to the packer.
The tubing has to fit in the casing through which the tubing extends, and this requirement limits the cross-sectional area that is available for fluid flow. Thus the throughput is restricted. In order to increase the throughput of an existing well, it is considered to remove the tubing so that the fluids flow through the casing. However, with no tubing well, control is nearly impossible. Moreover, when the fluids are aggressive, the casing can be affected.